Method and apparatus for substance delivery in system for supplying breathable gas

ABSTRACT

A substance delivery apparatus for use with a system for supplying breathable gas to a human or animal includes a sensor to measure the pressure of the supplied breathable gas and to detect inhalation by the human or animal; and a reservoir, a conduit, a pump, and a diaphragm to deliver the substance to the human or animal during inhalation at a pressure higher than the supplied pressure of the breathable gas.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 09/466,971, filed Dec.20, 1999, now U.S. Pat. No. 6,990,977, which is a continuation ofapplication Ser. No. 08/989,150, filed Dec. 12, 1997, now U.S. Pat. No.6,029,660, which claims priority to Australian Application No. PO4186,filed Dec. 12, 1996, each incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention relates to a substance delivery apparatus for usewith a system for supplying breathable gas to a human or animal.

BACKGROUND OF THE INVENTION

Treatment of Obstructive Sleep Apnea (CSA) with Continuous PositiveAirway Pressure (CPAP) flow generator systems involves the continuousdelivery of a breathable gas (generally air) pressurised aboveatmospheric pressure to a patient's airways via a conduit and a mask.CPAP pressures of 4 cm H₂O to 22 cm H₂O are typically used for treatmentof OSA, depending on patient requirements. Treatment pressures forassisted ventilation can range of up to 32 cm H₂O and beyond, againdepending on patient requirements.

For either the treatment of OSA or the application of assistedventilation or similar, the pressure of the gas delivered to patientscan be constant level, bi-level (in synchronism with patientinspiration) or auto setting in level. Throughout the specificationreference to CPAP is intended to incorporate a reference to any one of,or combinations of, these forms of pressurised gas supply.

It is difficult to administer substances such as medicines to patientsundergoing CPAP treatment without interrupting the treatment by removingthe gas supply mask.

It is an object of the present invention to ameliorate the abovedisadvantage.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides a substance deliveryapparatus for use with a system for supplying breathable gas to a humanor animal, the apparatus including:

means to measure the pressure of the supplied breathable gas;

means to detect inhalation by the human or animal; and

means to deliver the substance to the human or animal during inhalationat a pressure higher than the supplied pressure of the breathable gas.

In a second aspect the invention provides a method of delivering asubstance to a human or animal being supplied with breathable gas, themethod includes the steps of:

measuring the pressure of the supplied breathable gas;

detecting inhalation by the human or animal; and

delivering the substance to the human or animal during inhalation at apressure higher than the supplied pressure of the breathable gas.

The substance is preferably a medicinal substance and, desirably, in theform of a gas, mist, aerated suspension, jet, spray, gas mixture or thelike.

The substance is preferably delivered to the respiratory system of thehuman or animal and, in particular, to the nasal airways.

The supplied breathable gas is preferably pressurised above atmosphericpressure.

The system for supplying the breathable gas preferably includes apressurized gas flow generator in fluid communication with a mask wornby the human or animal is via a flexible conduit, and the inhalationdetection means includes an airflow sensor adapted to measure thevolumetric flow rate of the breathable gas passing through the conduitand generate a first input signal indicative of the breathable gas flowrate. The term mask is herein understood to include facemasks,nosemasks, mouthmask, apenditures in the vicinity of any of these masksand the like.

The first signal is preferably amplified by a first amplifer into asecond input signal also indicative of the gas flow rate. A derivativeof the first signal is also generated by a differentiating filter todetermine the acceleration or deceleration of the gas, which isindicative of inhalation or exhalation respectively, and is representedby a third input signal.

When the airflow sensor is disposed downstream of the mask's vent toatmosphere then inhalation can be detected by sensing a reversal of thedirection of the gas flow through the vent. Inhalation can also bedetected by sensing an interruption of the gas flow.

The apparatus preferably also includes means to measure the volume ofthe substance to be delivered to the human or animal.

The pressure measuring means is preferably a pressure transducerconnected to the conduit which is adapted to generate a fourth inputsignal indicative of the pressure of the gas in the conduit. The fourthinput signal is preferably amplified by a second amplifier into a fifthinput signal also indicative of the as pressure.

The substance delivery means is preferably a positive displacement pump,most preferably a diaphragm pump. The diaphragm pump is desirably influid communication with a substance reservoir via a one-way valveadapted to allow the substance to only pass from the reservoir to thepump. The pump is preferably also in fluid communication with the gassupply conduit via a one-way valve adapted to allow the substance toonly pass from the pump to the conduit.

The diaphragm of the pump is desirably displaced by a linear drive meanswhich, in one form, may take the form of an electromagnet. In otherforms, a rotary drive means such as an electric DC motor, an electric ACmotor, a stepper motor, or a brushless motor are used with a rotary tolinear converter interposed between the rotary drive means and thediaphragm pump.

The apparatus preferably also includes a first control system adapted toreceive the second, third and fourth input signals. The control systempreferably also includes input means adapted to allow the input of apredetermined sixth input indicative of the volume of the substance tobe delivered and a predetermined seventh input signal indicative of theamount by which the pressure of the delivered substance should exceedthe pressure of the supplied breathable gas. The first control system ispreferably adapted to receive the second, third, fifth, sixth andseventh input signals to calculate and generate a first output signalindicative of the amount of displacement of the linear or rotary drivemeans and a second output signal indicative of the direction of thedisplacement required to produce negative or positive pumping pressure.

The first and second output signals are preferably sent to a secondcontrol system which converts them into third and fourth output signalsindicative of drive means displacement and direction respectively, thethird and fourth output signals being compatible with the linear orrotary drive means.

Preferably, the first and second output signals are sent to a secondcontrol system adapted to convert them into third and fourth outputsignals indicative of drive means displacement and directionrespectively, the third and fourth output signals being compatible withthe linear or rotary drive means.

The input and output signals can be analog, digital or the like.

The described embodiments have been developed primarily for use indelivering medicinal substances co patients using Continuous PositiveAirway Pressure (CPAP) gas delivery systems in, for example, thetreatment of Obstructive Sleep Apnea (OSA) or similar sleep disorderbreathing conditions.

The invention will be described hereinafter with reference to theseapplications. However, it will be appreciated that the invention is norlimited to this particular field of use. As examples, the invention mayalso be used in conjunction with suitable mask and gas delivery systemsMoor other treatments such as assisted ventilation, assisted respirationor mechanical ventilation.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying figures in which:

FIG. 1 is a schematic diagram of a substance delivery apparatusaccording to a first embodiment of the invention;

FIG. 2 is a schematic diagram of a substance delivery apparatusaccording to a second embodiment of the invention;

FIG. 3 is a schematic diagram of a substance delivery apparatusaccording to a third embodiment of the invention;

FIG. 4 is a schematic diagram of the apparatus of FIG. 3 duringinhalation;

FIG. 5 is a schematic diagram of the apparatus shown in FIG. 3 duringexhalation;

FIG. 6 is a partial schematic diagram of a substance delivery apparatusaccording to a fourth embodiment of the invention; and

FIGS. 7 a, 7 b and 7 c are partial schematic diagrams of a substancedelivery apparatus according to a fifth embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring firstly to FIG. 1, there is shown a first embodiment of asubstance delivery apparatus 10 according to the invention. Theapparatus 10 is used with a system, indicated generally at 12, forsupplying air, indicated by arrow 14, to a human patient (not shown).The system 12 includes a pressurized gas flow generator 16 in fluidcommunication with a mask 18 via conduit 20. Mask 18 includes a gaswashout vent 19.

The apparatus 10 includes a means to measure the pressure of the air 14and to detect patient inhalation, in the form of an air flow sensor 22.The sensor 22 is interposed in the conduit 20 between the mask 18 andthe pressurised gas flow generator 16. The airflow sensor 22, in theform of a fixed orifice, is connected to an electronic flow transducer24. A variable orifice, venturi tube, Pitot tube or tubes bundle canalso be used to sense airflow. The transducer 24 generates a firstelectrical input signal 26 indicative of the flow rate of the air 14passing through the conduit 20 which is sent to a first flow signalprocessing amplifier and differentiating filter 28 which in turngenerates second and third input signals 30 and 32 respectively.

The second input signal 30 is an amplified version of the first inputsignal 26. The third input signal 32 is the derivative of the firstsignal 26, with acceleration and deceleration being respectivelyindicative of inhalation or exhalation. When a patient inhales theyapply suction to the air being delivered thus causing acceleration. Uponexhalation the air being delivered is obstructed by the exhaled airflowing in the opposite direction thus causing deceleration.

An air pressure transducer 34 is also connected to the conduit 20 andgenerates a fourth electrical input signal 36 indicative of the pressurein the conduit. The fourth signal 36 is delivered to an air pressureprocessing amplifier 38 which generates a fifth input signal 40 alsoindicative of the pressure in the conduit 20.

The second, third and fifth input signals 30, 32 and 40 are fed to afirst control system 42. The first control system 42 also receives sixthand seventh predetermined input signals 44 and 46 from manual inputs 48and 50 in the form of potentiometers accessible by a system operator.Variable resistors car, also be used as the manual inputs. The sixthinput signal 44 is indicative of the volume of substance to be deliveredto the mask during each inhalation cycle of the patient. The seventhsignal 46 is indicative of the amount by which the delivery pressure ofthe substance is to exceed the measured pressure of the air 14 in theconduit 20.

The means to deliver a substance 52 to the mask 18 includes a substancereservoir 54 connected by conduit 56 to diaphragm pump 58 having aflexible diaphragm 60. A one way valve 62 is interposed between thereservoir 54 and pump 58 and permits the substance 52 to only enter thepump 58. The pump 58 is in fluid communication with the conduit 20 byvirtue of conduit branch 64 and one way valve 66 which allows thesubstance 52 to pass from the pump 58 to the conduit 20.

The stroke of the diaphragm 60 is controlled by an electromagnet drivemeans 68, in the form of a magnet 70 connected to the centre of thediaphragm 60 and surrounded by electrical windings 72. The drive means68 are controlled by a second control system 74.

In response to receiving the second, third, fifth, sixth and seventhinput signals, the first control system 42 generates first and secondoutput signals 76 and 78, respectively indicative of the electromagnetdisplacement magnitude and direction. Displacement in the direction ofarrow 80 draws the substance 52 into the pump 58. Displacement in thedirection of arrow 82 causes the substance 52 to be pumped into theconduit branch 64 and thereafter the conduit 20. The output signals 76and 78 are received by the second control system 74 which issues thirdand fourth output signals 84 and 86 respectively, which are compatiblewith the drive means 68. The third output signal 84 is indicative of theamount of displacement of the electromagnet 68 and the fourth signal 86is indicative of the displacement direction.

In use, when the system is switched on, breathable air 14 is supplied bythe gas flow generator 16 to the mask 18 via the conduit 20) so thepatient may breathe.

As the patient inhales, an analogue to digital converter (not shown) inthe control system 42 samples the air flow information of the secondinput signal 30 over a few breaths and stores it in a memory (notshown). The stored values are integrated with respect, to the time ofthe inhalation portion of their respective breathing cycle. Theintegrated value is the tidal volume of each breath and is also storedin the memory. The stored values of the tidal volume are averaged over asmall number of breaths to provide an average value of the tidal volume.

From the average value of the tidal volume and the setting of the manualinput 48 the volume of the substance 52 (ie, the drug or gas) to bedelivered for each breath is calculated. The control system 42 alsocalculates the magnitude of the current to be applied to the windings 72of the diaphragm pump 58.

When the third input signal 32 indicates exhalation, the control systems42 and is 74 calculate and issue the third and fourth output signals 84and 86 to the windings 72. The direction of the current applied to thewindings 72 causes the magnet 70 and the diaphragm 60 to be displaced inthe direction of the arrow 80 to the position shown by phantom line 87.This movement of the diaphragm 60 draws the substance 52 past the oneway valve 63 and into the pump 58. The magnitude of the current appliedto windings 72 is proportional to the displacement of the diaphragm 60and also therefore the volume of gas drawn into the pump 58 which isdelivered to the patient during the next inhalation cycle. At the end ofthe patient exhalation cycle the current applied to the windings 72remains constant and the magnet 70 and diaphragm 60 remain as indicatedby line 87.

When the third input signal 32 indicates inhalation, the control system42 and 74 reverse the current flowing into the windings 72, therebydisplacing the magnet 70 and the diaphragm 60 in the direction indicatedby the arrow 82 to the position shown by phantom line 89. This movementforces the substance 52 from the pump 53 through the one way valve 68and conduit branch 64 into the mask 18.

The air pressure of the gas 14 in the conduit 20 is exceeded by thepressure of the substance pumped through conduit branch 64. The supplypressure of the substance 52 is calculated by the control system 42 andis the sum of the pressure measured by pressure transducer 34 in conduit20 and the pressure increment set by manual input 50. The substance 52is then delivered to the patient via the conduit 64 and the mask 18.

A second embodiment of the present invention is shown in FIG. 2, inwhich like reference numerals are used to indicate like features.

The first control system 42 of the second embodiment incorporates amicrocontroller 92 and a linear position transducer 94 connected to themagnet 70 to provide a feedback signal 96 indicative of the position ofthe magnet 70 and the diaphragm 60, to which it is connected.

The two manual inputs 48 and 50 are replaced by a digital control panel98 with: a three digit digital display 100; three push buttons: Mode102, “+” 104, “−” 106; and three LEDs to indicate the mode selected:Volume 108, Delivery Pressure 110 and Run 112.

The operation of this system is generally similar to the descriptionabove except where indicated below.

Successive depression of the Mode push button 102 cycles through thethree modes of operation: Volume, Delivery Pressure and Run.

When Volume or Delivery Pressure is selected, the digital display 100indicates the current setting of that parameter. This value may bemodified if required by operating either of the two push buttons “+” 104or “−” 106.

When Run is selected, the parameters stored in the memory of themicrocontroller 90 calculate the desired position of the magnet 70. Thisis then compared with the actual magnet position indicated by the linearposition transducer 94. Any difference produces an error signal that isused to correct the position of the magnet 70 to the desired position,

A third embodiment of the present invention is shown in FIGS. 3 to 5, inwhich like reference numerals are again used to indicate like features.In this embodiment, the flow processing amplifier and differentiatingfilter 28 again detects the onset of inhalation by sensing a change inthe rate of flow (ie. the acceleration or deceleration) of the gasflowing past the sensor 22.

The output signal 120 from the amplifier filter 28 of this embodiment isactive when the onset of inhalation is detected and remains active forthe duration of the inhalation portion of the breathing cycle. Theoutput signal 120 from the amplifier filter 28 is not active for theexhalation portion of the breathing cycle.

The output signal 120 is supplied to a driver stage 122 and an inverterstage 124.

When the output signal 120 is active, during inhalation, the driverstage 122 is active and applies power to an electromagnetic winding 126through a connection 128. When the output signal 120 is inactive, duringexhalation, the inverter stage 124 supplies a drive signal 130 to adriver stage 132. The driver sage 132 is activated and supplies power toan electromagnetic winding 134 through a connection 136.

A magnetic core 138 is located within the electromagnetic winding 126.Similarly, a magnetic core 140 is located within the electromagneticwinding 134.

The magnetic core 138 and the magnetic core 140 are connected by aconnecting rod 142 which is also connected to a sliding spool valve 144.

When the winding 126 is energised through the connection 128 themagnetic core 138 is displaced in the direction of arrow 150 and pullswith it the spool valve 144 and core 140.

When winding 134 is energised through connection 136 the magnetic core140 is displaced in the direction of arrow 152 and pulls with it thespool valve 144 and core 138.

The body 154 of the spool valve 144 is connected to the gas flowgenerator 16 through a branch conduit 156 connected to the conduit 20.

A diaphragm motor 157 is comprised of housing halves 158 and 160separated by a diaphragm 162 which defines cavities 164 and 166. Adiaphragm pump 168 is comprised of housing halves 170 and 172 separatedby a diaphragm 174 which defines cavities 176 and 178. The cavity 164 isconnected to the spool valve body 154 by a conduit 182. The cavity 166is connected to the spool valve body 154 by a conduit 184. The cavity176 is open to atmosphere. The cavity 178 is connected to the source 54of the substance 52 to be delivered by the conduit 56 and the one-wayvalve 62. The cavity 178 is also connected to the mask 18 by the conduit64 and the one-way valve 66.

The motor diaphragm 162 and the pump diaphragm 174 are connected by aconnecting rod 186. The connecting rod 186 passes through an air sealedbearing (not shown) between cavities 166 and 176.

An adjusting screw 188 is located on the top of housing halve 158.

With reference to FIG. 4, the operation of the apparatus will bedescribed during the inhalation portion of the breathing cycle.

As the patient start to inhale, the second output signal 120 from theflow processing amplifier 28 is set to active and activates the driverstage 122. The inverter stage 124 is inactive and magnetic core 140 isfree to move. The driver stage 122 supplies power to the electromagneticwinding 126 through connection 128. The magnetic core 138 is forced inthe direction of the arrow 150 and with it the spool valve 144. The air14 now flows from the branch conduit 156 into the spool valve body 154and is diverted by the spool valve 144 through the conduit 182 and intothe cavity 164. The pressure of the air entering the cavity 164 forcesthe motor diaphragm 162 in the direction of arrow 190 and with it thepump diaphragm 174. The cavity 178 is already filled with the substance52 to be delivered to the mask 18.

The displacement of the pump diaphragm 174 into the cavity 178 increasesthe substance pressure, closes the one-way valve 62, opens the one-wayvalve 66, and forces the substance 52 into the conduit 64. The conduit64 is in fluid communication with the conduit 20 and the mask 18 and thesubstance 52 is thereby delivered to the mask 18 and the patient.

With reference to FIG. 5, the operation of the apparatus will bedescribed during the exhalation portion of the breathing cycle.

As the patient start to exhale, the second output signal 120 from theflow processing amplifier 28 is set to inactive. The driver stage 122 isnot activated and power is not supplied to the electromagnetic winding126 through connection 128. The magnetic core 138 is therefore free tomove. As the output signal 120 from the flow processing amplifier 28 isnow inactive, the inverter stage 124 turns its output signal to activeand activates the driver stage 132. The driver stage 132 supplies powerto the electromagnetic winding 134 through the connection 136 and themagnetic core 140 is forced in the direction of the arrow 152 and withit the spool valve 144. The air flows from the branch conduit 156 intothe spool valve body 154 and is diverted by the spool valve 144 throughthe conduit 184 into the cavity 166. The pressure of the air in thecavity 166 forces the motor diaphragm 162 in the direction of arrow 192and with it the pump diaphragm 174. The displacement of pump diaphragm174 into cavity 176 produces a vacuum in cavity 178, closes the one-wayvalve 66, opens the one-way valve 62, and draws the substance 52 throughthe conduit 56 into the cavity 178.

The movement of the motor diaphragm 162 and pump diaphragm 174 islimited by the adjusting screw 188. The setting of the screw 188 governsthe maximum displacement of the motor diaphragm 162 and pump diaphragm174 in direction of the arrow 192, therefore controlling the volume ofthe substance 52 able to be drawn into the cavity 178 for delivery tothe patient during the next inhalation.

The pump diaphragm 174 is smaller in area than the motor diaphragm 162.Accordingly, a given pressure supplied to motor diaphragm 162 willproduce a greater pressure from the pump diaphragm 174. Therefore, thepressure delivered by the pump diaphragm 174 into the conduit 64 and thepatient mask 18 will always exceed the pressure of the gas in theconduit 20. The ratio between the pressure in the conduit 20 and theconduit 64 is proportional to the ratio between the area of thediaphragms 174 and 162.

In another embodiment (not shown) the diaphragm motor 157 is replaced byan electric motor, such as a stepper motor, controlled by a controlsystem to provide more accurate delivery of the substance 52.

A fourth embodiment of the present invention is shown in FIG. 6, inwhich like reference numerals are again used to indicate like features.This embodiment is for use in conjunction with a bi-level CPAP flowgenerator (not shown) that delivers breathable gas at a relatively hightreatment pressure to the mask during patient inhalation and at arelatively low treatment pressure during exhalation. The applicantmarkets such a bi-level system under the trade mark VPAP.

This embodiment includes a motor cylinder 200 having a slidable piston202 which defines cavities 204 and 206. A pump cylinder 208 is alsoprovided having a slidable piston 210 which defines cavities 212 and214. The pistons 202 and 210 are connected by a connecting rod 216 whichpasses through an air sealed bearing 218.

The cavity 204 is connected to the conduit 20 by the branch conduit 156.The cavities 206 and 212 are open to atmosphere. The cavity 214 isconnected to the source 54 of the substance 52 by Me conduit 56 via theone-way valve 62. The cavity 214 is also connected to the mask 18 by theconduit 64 and the one-way valve 66.

The pistons are biased in the direction of arrow 220 by a spring 222.

The operation of the apparatus shown in FIG. 6 will now be described.During exhalation, relatively low pressure gas is passing throughconduit 20 which generates only a small amount of force on the piston202. The spring 222 overcomes this force and drives the pistons 202 and210 in the direction of the arrow 220 thereby creating a vacuum incavity 214. The vacuum draws the substance 52 past the one-way valve 62and into the cavity 214.

During inhalation, relatively high pressure gas is passing through theconduit 20 which generates enough force on the piston 202 to overcomethe spring 222 and drive the pistons 202 and 210 in the direction ofarrow 224. This forces the substance in the cavity 214 past the one-wayvalve 66 and into the mask 18 via the conduit 64.

The surface area of the piston 202 is larger than that of the piston 210and the pressure generated by the piston 210 will therefore exceed thatapplied to the piston 202. Accordingly, the substance delivery pressurewill always exceed the pressure produced by the flow generator duringthe inhalation phase of the breathing cycle. The ratio between thesurface areas of the pistons 202 and 210 is proportional to the ratiobetween the breathable gas pressure and the substance delivery pressure.

A fifth embodiment of the present invention is shown in FIGS. 7 a, 7 band 7 c. The fifth embodiment is essentially a modification of thefourth embodiment so it will work with a constant pressure flowgenerator.

The fifth embodiment includes a control valve 230 interposed between theconduit 20 and the motor cylinder 200. The valve 230 includes an inlet232 connected to the conduit 20, a first outlet 234 connected to thecavity 204 and a second outlet 236 open to atmosphere.

The valve 230 is controlled by an electronic valve controller 238 whichreceives a signal 240 indicative of inhalation or exhalation, asdiscussed with respect to earlier embodiments.

When the signal 240 indicates inhalation, the controller 238 causes thevalve 230 to move to the position indicated in FIG. 7 b. In thisposition, the air 14 is diverted into the cavity 204 causing the pistonsto move in the direction of the arrow 224 and the substance 52 to bepumped into the mask 18, as previously described.

When the signal 240 indicates exhalation, the controller 238 causes thevalve 230 to move to the position shown in FIG. 7 c. In this position,the air in the cavity 204 is vented to atmosphere as the pistons move inthe direction of the arrow 220 under the influence of the spring 2227.As previously described, this movement also causes the substance 52 tobe drawn into the cavity 214.

The present invention, at least in preferred forms, provides a measuredsubstance dose to a human or animal during inspiration only, therebygreatly reducing drug wastage.

The preferred apparatus also allows the substance to be delivered to thepatient without interrupting CPAP, or similar treatment, or sleep,thereby increasing patient comfort and convenience.

The preferred apparatus also obviates the need for a patient to rememberto take medicine.

The invention has been described with reference to specific examples.However, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms.

1. A substance delivery apparatus for use with a system for supplyingbreathable gas pressurized above atmospheric pressure to a human oranimal, the apparatus including: means for measuring the pressure of asupplied breathable gas; and means for delivering a substance to thehuman or animal only during inhalation at a pressure that exceeds themeasured pressure of a supplied pressure of the breathable gas by apredetermined pressure difference.
 2. An apparatus as claimed in claim1, wherein the substance is a medicinal substance.
 3. An apparatus asclaimed in claim 1, wherein the substance is in the form of a gas, mist,aerated suspension, jet, spray, or a gas mixture.
 4. An apparatus asclaimed in claim 1, further including means for measuring a volume ofthe substance to be delivered to the human or animal.
 5. An apparatus asclaimed in claim 1, wherein the pressure of the supplied breathable gasis typically between 4-32 cmH₂O.
 6. An apparatus as claimed in claim 1,wherein the means for delivering the substance is adapted to deliver thesubstance to a respiratory system of the human or animal.
 7. Anapparatus as claimed in claim 6, wherein the means for delivering thesubstance is adapted to deliver the substance to nasal airways of thehuman or animal.
 8. An apparatus as claimed in claim 1, wherein themeans for measuring the pressure is a pressure transducer adapted to beconnected to a conduit in fluid communication with a pressurized gasflow generator and a mask adapted to be worn by the human or animal,said transducer being adapted to generate a fourth input signalindicative of pressure of the breathable gas in the conduit.
 9. Anapparatus as claimed in claim 8, including an amplifier to amplify thefourth input signal into a fifth input signal also indicative of gaspressure in the conduit.
 10. An apparatus as claimed in claim 1, furthercomprising means for detecting inhalation by the human or animal.
 11. Anapparatus as claimed in claim 10, wherein the means for detectinginhalation includes an airflow sensor adapted to measure a volumetricflow rate of the breathable gas passing through a flexible conduit influid communication with a pressurized gas flow generator and a maskadapted to be worn by the human or animal and being adapted to generatea first input signal indicative of the breathable gas flow rate.
 12. Anapparatus as claimed in claim 11, further including an amplifier toamplify the first input signal into a second input signal alsoindicative of the breathable gas flow rate.
 13. An apparatus as claimedin claim 11, further including a differentiating filter to derive thefirst signal into a third input signal indicative of acceleration ordeceleration of the breathable gas to thereby indicate inhalation orexhalation respectively.
 14. An apparatus as claimed in claim 11,wherein the airflow sensor is adapted to be disposed downstream of a gaswashout vent of the mask such that inhalation can be detected by sensinga reversal of direction of the breathable gas flow through the vent. 15.An apparatus as claimed in claim 14, wherein the airflow sensor isadapted to detect inhalation by sensing an interruption of thebreathable gas flow through the vent.
 16. An apparatus as claimed inclaim 1, wherein the means for delivering a substance is a positivedisplacement pump.
 17. An apparatus as claimed in claim 16, wherein thepositive displacement pump is a diaphragm pump.
 18. An apparatus asclaimed in claim 17, wherein the diaphragm pump is in fluidcommunication with a substance reservoir via a one-way valve adapted toallow the substance to only pass from the reservoir to the diaphragmpump.
 19. An apparatus as claimed in claim 17, wherein the diaphragmpump is adapted to be in fluid communication with the gas supply conduitvia a one-way valve adapted to allow the substance to only pass from thediaphragm pump to the conduit.
 20. An apparatus as claimed in claim 17,wherein the diaphragm pump is displaced by a linear drive.
 21. Anapparatus as claimed in claim 20, wherein the linear drive is anelectromagnet.
 22. An apparatus as claimed in claim 17, wherein adiaphragm of the diaphragm pump is displaced by a rotary to linearconverter driven by a rotary drive.
 23. An apparatus as claimed in claim22, wherein the rotary drive is one of an electric DC motor, an electricAC motor, a stepper motor or a brushless motor.
 24. A method ofdelivering a substance to a human or animal being supplied withbreathable gas pressurized above atmospheric pressure, the methodincluding: measuring the pressure of a supplied breathable gas; anddelivering a substance to the human or animal only during inhalation ata pressure that exceeds the pressure of a supplied pressure of thebreathable gas by a predetermined pressure difference.
 25. A method asclaimed in claim 24, wherein the delivery includes treatment ofobstructive sleep apnea with continuous positive airway pressure (CPAP).26. A method as claimed in claim 24, wherein the pressurized breathablegas is provided to the patient at a first treatment pressure duringinhalation and a second treatment pressure during exhalation, whereinthe first treatment pressure is higher than the second treatmentpressure and the method further comprises delivering the substance tothe patient only during the delivery of the first treatment pressure.27. A method as claimed in claim 24, wherein the substance is amedicinal substance.
 28. A method as claimed in claim 27, wherein thesubstance is in the form of a gas, mist, aerated suspension, jet, spray,or a gas mixture.
 29. A method as claimed in claim 24, wherein thesubstance is delivered to a respiratory system of the human or animal.30. A method as claimed in claim 29, wherein the substance is deliveredto nasal airways of the human or animal.
 31. A method as claimed inclaim 24, including measuring volume of the substance to be delivered tothe human or animal.
 32. A method as claimed in claim 31, wherein thebreathable gas pressure is measured with a pressure transducer adaptedto generate a fourth input signal indicative of the breathable gaspressure.
 33. A method as claimed in claim 32, including amplifying thefourth input signal into a fifth input signal also indicative of thebreathable gas pressure.
 34. A method as claimed in claim 24, includingmeasuring the volumetric flow rate of the breathable gas with an airflowsensor and generating a first input signal indicative of the breathablegas flow rate.
 35. A method as claimed in claim 34, including amplifyingthe first signal into a second signal also indicative of the breathablegas flow rate.
 36. A method as claimed in claim 34, includingdifferentiating the first signal into a third signal indicative ofbreathable gas acceleration or deceleration to indicate inhalation orexhalation respectively.
 37. A method as claimed in claim 24, whereinthe substance is delivered to the human or animal using a positivedisplacement pump.
 38. A method as claimed in claim 37, wherein thepositive displacement pump is a diaphragm pump.
 39. A method as claimedin claim 38, wherein the diaphragm pump is in fluid communication with asubstance reservoir via a one-way valve adapted to allow the substanceto only pass from the reservoir to the diaphragm pump.
 40. A method asclaimed in claim 38, wherein the diaphragm pump is adapted to be influid communication with the gas supply conduit via a one-way valveadapted to allow the substance to only pass from the diaphragm pump tothe conduit.
 41. A method as claimed in claim 38, wherein the diaphragmpump is displaced by a linear drive.
 42. A method as claimed in claim41, wherein the linear drive is an electromagnet.
 43. A method asclaimed in claim 38, wherein the diaphragm pump is displaced by a rotaryto linear converter driven by a rotary drive.
 44. A method as claimed inclaim 43, wherein the rotary drive is one of an electric DC motor, anelectric AC motor, a stepper motor or a brushless motor.
 45. A substancedelivery apparatus for use with a system for supplying breathable gaspressurized above atmospheric pressure to a human or animal, theapparatus including: a pressure transducer to measure pressure of asupplied breathable gas; and a positive displacement pump to deliver asubstance to the human or animal only during inhalation at a pressurethat exceeds the measured pressure of the supplied breathable gas by apredetermined pressure difference.
 46. An apparatus as claimed in claim45, wherein the substance is a medicinal substance.
 47. An apparatus asclaimed in claim 45, wherein the substance is in the form of a gas,mist, aerated suspension, jet, spray, or a gas mixture.
 48. An apparatusas claimed in claim 45, further including signals indicative of volumeof the substance to be delivered to the human or animal.
 49. Anapparatus as claimed in claim 45, wherein the supplied breathable gas isprovided to the patient at a first treatment pressuring duringinhalation and a second treatment pressure during exhalation, whereinthe first treatment pressure is higher than the second treatmentpressure and the positive displacement pump is configured to deliver thesubstance to the patient only during the delivery of the first treatmentpressure.
 50. An apparatus as claimed in claim 45, wherein the substanceis delivered to a respiratory system of the human or animal.
 51. Anapparatus as claimed in claim 50, wherein the substance is delivered tonasal airways of the human or animal.
 52. An apparatus as claimed inclaim 45, wherein the pressure transducer is connected to a conduit influid communication with a pressurized gas flow generator and a maskadapted to be worn by the human or animal of the system for supplyingbreathable gas, said transducer being adapted to generate a fourth inputsignal indicative of the pressure of the breathable gas in the conduit.53. An apparatus as claimed in claim 52, including an amplifier toamplify the fourth input signal into a fifth input signal alsoindicative of the breathable gas pressure.
 54. An apparatus as claimedin claim 45, further comprising an airflow sensor to detect inhalationby the human or animal.
 55. An apparatus as claimed in claim 54, whereinthe airflow sensor further measures a volumetric flow rate of thebreathable gas passing through a flexible conduit in fluid communicationwith a pressurized gas flow generator and a mask adapted to be worn bythe human or animal, and generates a first input signal indicative ofthe breathable gas flow rate.
 56. An apparatus as claimed in claim 55,further including an amplifier adapted to amplify the first input signalinto a second input signal also indicative of the breathable gas flowrate.
 57. An apparatus as claimed in claim 55, further including adifferentiating filter adapted to derive the first signal into a thirdinput signal indicative of acceleration or deceleration of thebreathable gas to thereby indicate inhalation or exhalationrespectively.
 58. An apparatus as claimed in claim 55, wherein theairflow sensor is disposed downstream of a gas washout vent of the masksuch that inhalation can be detected by sensing a reversal of thedirection of the breathable gas flow through the vent.
 59. An apparatusas claimed in claim 58, wherein inhalation is detected by sensing aninterruption of the breathable gas flow through the vent.
 60. Anapparatus as claimed in claim 45, wherein the positive displacement pumpis a diaphragm pump.
 61. An apparatus as claimed in claim 60, whereinthe diaphragm pump is in fluid communication with a substance reservoirvia a one-way valve adapted to allow the substance to only pass from thereservoir to the diaphragm pump.
 62. An apparatus as claimed in claim60, wherein the diaphragm pump is adapted to be in fluid communicationwith the gas supply conduit via a one-way valve adapted to allow thesubstance to only pass from the diaphragm pump to the conduit.
 63. Anapparatus as claimed in claim 60, wherein the diaphragm pump isdisplaced by a linear drive.
 64. An apparatus as claimed in claim 63,wherein the linear drive is an electromagnet.
 65. An apparatus asclaimed in claim 60, wherein a diaphragm of the diaphragm pump isdisplaced by a rotary to linear converter driven by a rotary drive. 66.An apparatus as claimed in claim 65, wherein the rotary drive is one ofan electric DC motor, an electric AC motor, a stepper motor and abrushless motor.
 67. A substance delivery system for supplyingbreathable gas pressurized above atmospheric pressure to a human oranimal, the system including: a pressurized gas flow generator in fluidcommunication with a mask adapted to be worn by the human or animal viaa flexible conduit; a pressure transducer adapted to measure thepressure of a supplied breathable gas; and a positive displacement pumpadapted to deliver a substance within the flexible tube to the human oranimal only during inhalation at a pressure that exceeds the measuredpressure of the supplied breathable gas by a predetermined pressuredifference.
 68. An apparatus as claimed in claim 67, wherein the flowgenerator is configured to generate a first treatment pressure duringpatient inhalation and a second treatment pressure during patientexhalation, wherein the first treatment pressure is higher than thesecond treatment pressure and the positive displacement pump is adaptedto deliver the substance to the patient only during the delivery of thefirst treatment pressure.
 69. An apparatus as claimed in claim 67,further comprising an airflow sensor adapted to detect inhalation by thehuman or animal.
 70. A system as claimed in claim 69, further includinga substance reservoir to store the substance, wherein the airflow sensoris also configured to detect exhalation by the human or animal, whereinthe substance reservoir is configured to provide the substance to thepositive displacement pump during exhalation of the human or animal, andwherein the substance is delivered from the positive displacement pumpto the human or animal during inhalation of the human or animal.